\$\begingroup\$Any requirement about A, B and C being different strings? For example, can the three strings be the same? If the program prints a newline after the output, can we not count that?\$\endgroup\$
– Luis MendoJul 12 '17 at 20:38

\$\begingroup\$It is not required A, B, C being different. Newlines are counted as part of output so newlines in the string are part of the program.\$\endgroup\$
– BlexJul 13 '17 at 8:56

2 Answers
2

That's right, it's the same program three times over! When run in any of the above languages, it prints the source code twice, which is the other two programs concatenated.

How It Works:

Befunge code:
"r j '!_@#,k.'g00
" Wrapping string literal over code
r Reflect the pointer
" Wrapping string literal
g00 Fetch " from cell 0,0
,k.' Print 47 characters
_@# If the next character is 0, exit
! Otherwise, set it to 0
j ' And jump back to the beginning
Gol><> code:
"r75*1-47*0. \`/KH
" Wrapping string literal
r Reverse stack
75*1- Push "
47*0. Jump to cell 28,0
\ Continue right
`/K Duplicate the top 47 characters on the stack
H Halt and output stack contents
Wumpus code:
"r75*1-47*0.@o&r84#o&]=74#]=\
"r75*1-47*0. Exact same function as the ><> code, but with a bouncing string literal
\ Reflect left
]= Push a copy of the " to the bottom of the stack
74# Push 47
]= Push a copy of the 47 to the bottom of the stack
o& Print the top 47 characters
84# Push a '0' to make up for the missing 0 at the end
o&r Reverse the stack and print the top 47 characters
@ And terminate

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